The "Man in the Middle Attack" is a security vulnerability which has to do with intercepting communications without being observed. It has been around, oh, at least 500 years or so.
MITM attacks are always interesting. Did you see the recent MI (Mission Impossible) movie? There's a great MITM attack in that movie (on the 130th floor of the tallest building in the world, no less!).
In the MI movie, two different criminal organizations are conducting a business transaction, in which one organization is selling information and the other is paying money. The MI team arranges a clever deception, pretending to be the seller of the information to the buyer, and pretending to be the purchaser of the information to the seller. The trick works because neither the buyer nor the seller know each other ahead of time, and cannot successfully authenticate each other, so they fall for the trick.
It's classic MI stuff; they used to pull it off in the original TV series oh-so-many years ago. But I find that it's often easier to recognize techniques like this when they are portrayed in an entertaining fashion, as opposed to the more dry, if more technically correct, format in which they are usually discussed.
So, I happened to be reading Andrew ("bunnie") Huang's fascinating paper on MITM attacks in HDCP video transmission. It's deep and complex work, and not easy going; the slides are a much easier way to get an overview of what's going on here.
As bunnie observes, this particular attack is less about cryptography (though there is plenty of that going on here), than about understanding the policy and cultural frameworks within which cryptography and digital rights management are used:
While the applications of video overlay are numerous, the basic scenario is that while you may be enjoying content X, you would also like to be aware of content Y. To combine the two together would require a video overlay mechanism. Since video overlay mechanisms are effectively banned by the HDCP controlling organization, consumers are slaves to the video producers and distribution networks, because consumers have not been empowered to remix video at the consumption point.
Reading bunnie's work is always engrossing, even though most of it goes way over my head. That's the thing about trying to learn stuff: often you work and work and work and maybe you just get a little bit smarter, but that's certainly better than not getting smarter at all.
So, thank you bunnie, for the informative writeup of your work!